Introduction%20to%20Metabolism

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Introduction to Metabolism

• Ch. 8 AP Biology

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Metabolism

• Definition The totality of an organisms
  chemical processes
• An organisms chemical reactions are arranged
  into intricately branched pathways
• Metabolic pathway
• Alters molecules by a series of steps.
• Each step is selectively accelerated by a
  particular enzyme

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Catabolic Pathways

• Result in the breakdown of complex molecules into
  simpler compounds.
• Example Cellular respiration
• Glucose is broken down into CO2 and H2O
• Energy that was stored in the chemical bonds of
  glucose becomes available to do work for the cell.

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Anabolic Pathways

• Pathways that consume energy to build complicated
  molecules from simpler molecules
• Example making proteins from amino acids
• Example Photosynthesis

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Organisms are Energy Transformers

• Energy
• The ability to do work.
• Two Types of Energy
• Kinetic
• Energy of motion
• Example light
• Potential
• Stored energy
• Possessed by matter because of its location or
  structure
• Chemical energy especially important in biology
• Transformation of energy from kinetic to
  potential and back again is essential to life.
• Living things do this all the time!

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Thermodynamics

• The study of energy transformations
• Organisms are open systems
• They absorb energy from the environment
• They release heat into the environment

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Laws of Thermodynamics

• 1st Law of Thermodynamics
• Energy can be transformed, but it cannot be
  created or destroyed
• 2nd Law of Thermodynamics
• Energy transformation increases the entropy of
  the universe
• Entropy measure of disorder or randomness
• Example of entropy heat
• In most energy transformations, ORDERED forms of
  energy are converted to HEAT
• Conversion of energy to different forms does NOT
  violate 1st law.
• Order of life does NOT violate the 2nd Law.
• Entropy of the UNIVERSE, as a whole, is
  increasing in spite of the order that living
  things maintainat least for a while.
• QUANTITY of energy in the universe is constant
• QUALITY of energy is not.

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Free Energy

• Spontaneous change
• Change that can occur without outside help
• Can be harnessed to perform work
• Causes stability of a system to increase
• Unstable systems tend to change to become more
  stable
• A process can occur spontaneously ONLY if it
  increases the entropy of the universe.

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Free Energy

• Definition
• Portion of a systems energy that can perform
  work when temperatures are uniform in the system
• Symbol
• G

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Concept of Free Energy helps us determine if a
process can occur spontaneously.

• G is a measure of a systems instability
• Its tendency to change to move to a more stable
  state.
• Systems that are rich in energy are unstable
• More complex molecules are rich in energy and
  therefore, unstable.
• Those systems that tend to change spontaneously
  to a more stable state are those that have high
  energy and thus low entropy.
• In any spontaneous process, the G of a system
  DECREASES
• Change in G would be negative.

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Free Energy and Chemical Reactions

• As a chemical reaction moves toward equilibrium,
  free energy of the reactants and products
  decreases.
• Free energy INCREASES when the reaction is moved
  away from equilibrium.
• At equilibrium, change in G 0
• At equilibrium, a chemical reaction performs NO
  work.
• A process is spontaneous and CAN perform work
  when it is SLIDING TOWARD equilibrium
• Movement AWAY from equilibrium is NONspontaneous
  and occurs ONLY with the help of an OUTSIDE
  ENERGY source.

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Exergonic Reactions

• Energy outward
• Proceeds with a net release of free energy
• Change in G is negative
• CELLULAR RESPIRATION

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Endergonic Reaction

• Energy inward
• STORES free energy in molecules
• Change in G is positive
• NONspontaneous
• PHOTOSYNTHESIS
• If a chemical process is EXERGONIC in one
  direction, it must be ENDERGONIC in the reverse
  direction.

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Cells at equilibrium

• Are DEAD.
• Thus, it is advantageous to sustain
  DISequilibrium
• Product of one reaction is not allowed to
  accumulate, but instead becomes a reactant in the
  next step along some metabolic pathway.

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ATP and Cellular Work

• Cells do three kinds of work
• Mechanical
• Moving stuff cilia for example
• Transport
• Moving molecules against concentration gradient
• Chemical
• Pushing of reactions that would NOT occur
  spontaneously
• ATP is the immediate source of energy that powers
  cellular work

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ATP

• Adenosine Triphosphate

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Hydrolysis of ATP

• Breaking of bonds between the phosphate groups of
  the ATP tail
• Energy is released
• Molecules of ADP and Pi (inorganic phosphate) are
  left behind
• EXERGONIC
• Change in G is 7.3 Kcal/mol
• Phosphate bonds are NOT unusually strong in
  fact, they are fragile
• All 3 phosphate groups are negatively charged
• Triphosphate tail is like a loaded spring
• ADP and Pi are more stable than ATP

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ADP and Pi are Renewable

• ATP is made from the ADP and Pi that result when
  ATP is used by the cell
• If ATP were NOT recyclable in this way, humans
  would have to consume their body weight in ATP
  each day.
• The regeneration of ATP from ADP and Pi is
  endergonic
• 7.3 kcal/mol are required
• Cellular Respiration is the process that makes
  the energy to regenerate ATP
• Energy is RELEASED from the breakdown of a
  GLUCOSE molecule to do this

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ATP and Pi are Renewable
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ENZYMES

• Just because a reaction is spontaneous, does NOT
  mean it is fast.
• Many chemical reactions happen so slowly that
  they are imperceptible.
• Enzymes are CATALYSTS.
• Speeds the rate of a chemical reaction without
  being consumed in the reaction

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Activation Energy

• Initial energy required to get a reaction started
• Initial energy required to break bonds
• Acts as a barrier that must be overcome in order
  for the reaction to occur
• Someone has to push the boulder off the top of
  the mountain in order for it to fall.
• Heat is one way to provide activation energy
• Speed up movement of molecules
• Increase collisions stress bonds
• However, heat is BAD for cells
• Enzymes LOWER activation energy without
  increasing temperature

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Activation Energy
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ENZYMES

• Substrate substance upon which the enzyme acts
• The substrate will undergo change to become
  product
• The enzyme remains unchanged
• Can be used again and again

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Fit of Enzymes with Substrates

• Enzymes are complexly shaped
• Active site
• Region of enzyme that interacts with substrate
• Shape of active site is critical to function
• Induced fit
• Enzyme fits substrate like a clasping handshake
• Enzyme is induced by substrate to change its
  shape to fit the substrate precisely/snugly
• Not rigid like a key and lock

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Enzyme Action

• Enzyme-substrate complex forms
• Substrate is held at the active site by
• hydrogen bonds ionic bonds, etc.
• Induced fit between enzyme and substrate occurs
• Enzymes catalyze reactions in a variety of ways
• Stress bonds of substrate making them easier to
  break
• Bringing two or more substrates together making
  it more likely they will bond
• Enzyme releases products
• Enzyme will go on to act again and again
• 1000 molecules/sec!
• An enzyme is saturated when it is catalyzing the
  maximum number of reactions it can
• Only way to speed reaction would be to add more
  enzyme

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Enzyme Action
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Affects of Environment on Enzymes

• Denature enzyme loses its shape
• Shape is CRITICAL to function
• If misshapen, the enzyme will not work
• Factors that denature enzymes
• Increase in Temperatures
• pH
• There are others.
• Other environmental factors may not denature
  enzymes, but still affect their ability to
  catalzye
• Decrease in Temperature
• Lowers speed of molecules
• Lowers number of collisions
• Lowers rate of reaction

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Cofactors

• Nonprotein helpers of enzymes
• Molecules that help enzymes do their jobs
• Inorganic
• Metal atoms zinc, copper, iron
• Organic
• Coenzymes - vitamins

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Enzyme Inhibitors

• A chemical that specifically and selectively
  inhibits a particular enzyme
• Helps control enzyme activity

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CONTROL OF METABOLISM

• Metaboic Pathways
• Also called biochemical pathways
• The product of one reaction becomes the reactant
  for the next reaction until the needed product is
  made
• Many steps
• Each step is catalyzed by a particular enzyme
• These pathways can be controlled by
• Switching on and off the genes that encode
  specific enzymes (genetic control)
• Regulating the activity of enzymes once they are
  made (focus of our study now)

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Allosteric Enzymes

• Enzyme has two active sites
• normal active site that interacts with
  substrate
• 2nd active site (or receptor region) that binds
  with some molecule that affects activity of the
  enzyme itself.
• 2nd site may be used to inhibit or stimulate an
  enzymes activity

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Feedback Inhibition

• End product of a biochemical pathway acts as
  inhibitor of an enzyme within the pathway
• Switches OFF the metabolic pathway
• Prevents the cell from wasting chemical resources
  if the product of the pathway is already in good
  supply

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Cooperativity

• Enzymes can also be stimulated to go to work
• Cooperativity amplifies the response of an enzyme
  to its substrate

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Organelles help to ORDER metabolism

• Enzymes are often isolated from different parts
  of the cell by the organelles that contain them
• Helps control sequence of chemical reactions
• Keeps incompatible processes separated
• Allows for more efficient reaction results